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- Fisher, R., Radford, B.T., Knowlton, N., Brainard, R.E., Michaelis, F.B., and Caley, M.J. Global mismatch between research effort and conservation needs of tropical coral reefs. Conservation Letters 4(1): 64-72, 2011.
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Tropical coral reefs are highly diverse and globally threatened. Management to ensure their persistence requires sound biological knowledge in regions where coral reef biodiversity and/or the threats to it are greatest. This paper uses a novel text analysis approach and Google Maps (TM) to examine the spatial coverage of scientific papers on coral reefs listed in Web of Science (R). Results show that research is highly clumped spatially, positively related to per capita gross domestic product, negatively related to coral species richness, and unrelated to threats to coral reefs globally; indicating a serious mismatch between conservation needs and the knowledge required for effective management. Greater research effort alone cannot guarantee better conservation outcomes, but given some regions of the world (e.g., central Indo-Pacific) remain severely understudied, priority allocation of resources to fill such knowledge gaps should support greater adaptive management capacity through the development of an improved knowledge base for reef managers.
- McClanahan, T.R. Human and coral reef use interactions: From impacts to solutions? Journal of Experimental Marine Biology and Ecology 408(1-2): 3-10, 2011.
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The literature on coral reefs and human resource use or fishing is reviewed less from the perspective of summarizing findings but more from the sociological perspective of what scientists chose to study, publish, and cite in journal articles. The motivation was to determine if coral reef science is generating information needed to solve the coral reef climate and fisheries crisis that has been publicized in many of the highest visibility and cited publications. The social-ecological system of coral reefs involves the environment, the ecosystem, human harvesting and social organization and the policies that arise from their interaction. Regardless of the focus and findings of any science investigation on this system, recommendations for management are limited, and include restrictions on space, time of use, effort, gear, species, size, and gender. Evaluating the scientific journal literature in the Scopus database on these restrictions indicates a disparity in focus for both publications and citations. The greatest number of scientists and citations are focused on spatial closures and fishing effort, effort seen as the problem and closures the solution. The other restrictions, that represent less extreme forms of management and have lower short-term social costs and trade offs, are not well studied and, when studied, investigated by either a small group of associated colleagues or transient one-publication investigators. When the values, selectivity, and incentives of scientists conflict with resource users desires for knowledge, incentives, and profits the resulting divide can weaken the social relevance and applicability of science and delay real-world problem solving. Societal engagement, acceptance, objectivity, and finding solutions are likely to increase if scientific effort is spread more evenly across this full spectrum of management restrictions and more components of the social-ecological system.
- Vroom, P.S. "Coral dominance": A dangerous ecosystem misnomer? Journal of Marine Biology 2011: art. 164127, 2011.
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Over 100 years ago, before threats such as global climate change and ocean acidification were issues engrossing marine scientists, numerous tropical reef biologists began expressing concern that too much emphasis was being placed on coral dominance in reef systems. These researchers believed that the scientific community was beginning to lose sight of the overall mix of calcifying organisms necessary for the healthy function of reef ecosystems and demonstrated that some reefs were naturally coral dominated with corals being the main organisms responsible for reef accretion, yet other healthy reef ecosystems were found to rely almost entirely on calcified algae and foraminifera for calcium carbonate accumulation. Despite these historical cautionary messages, many agencies today have inherited a coral-centric approach to reef management, likely to the detriment of reef ecosystems worldwide. For example, recent research has shown that crustose coralline algae, a group of plants essential for building and cementing reef systems, are in greater danger of exhibiting decreased calcification rates and increased solubility than corals in warmer and more acidic ocean environments. A shift from coral-centric views to broader ecosystem views is imperative in order to protect endangered reef systems worldwide.
- Hargreaves-Allen, V., Mourato, S., and Milner-Gulland, E.J. A global evaluation of coral reef management performance: Are MPAs producing conservation and socio-economic improvements? Environmental Management 47(4): 684-700, 2011.
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There is a consensus that Marine Protected Area (MPA) performance needs regular evaluation against clear criteria, incorporating counterfactual comparisons of ecological and socio-economic performance. However, these evaluations are scarce at the global level. We compiled self-reports from managers and researchers of 78 coral reef-based MPAs world-wide, on the conservation and welfare improvements that their MPAs provide. We developed a suite of performance measures including fulfilment of design and management criteria, achievement of aims, the cessation of banned or destructive activities, change in threats, and measurable ecological and socio-economic changes in outcomes, which we evaluated with respect to the MPA's age, geographical location and main aims. The sample was found to be broadly representative of MPAs generally, and suggests that many MPAs do not achieve certain fundamental aims including improvements in coral cover over time (in 25% of MPAs), and conflict reduction (in 25%). However, the large majority demonstrated improvements in terms of slowing coral loss, reducing destructive uses and increasing tourism and local employment, despite many being small, underfunded and facing multiple large scale threats beyond the control of managers. However spatial comparisons suggest that in some regions MPAs are simply mirroring outside changes, with demonstrates the importance of testing for additionality. MPA benefits do not appear to increase linearly over time. In combination with other management efforts and regulations, especially those relating to large scale threat reduction and targeted fisheries and conflict resolution instruments, MPAs are an important tool to achieve coral reef conservation globally. Given greater resources and changes which incorporate best available science, such as larger MPAs and no-take areas, networks and reduced user pressure, it is likely that performance could further be enhanced. Performance evaluation should test for the generation of additional ecological and socio-economic improvements over time and compared to unmanaged areas as part of an adaptive management regime.
- Graham, N.A.J. et al. From microbes to people: Tractable benefits of no-take areas for coral reefs. Oceanography and Marine Biology: An Annual Review (49): 105-136, 2011.
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The number of no-take marine protected areas (here referred to as no-take areas, NTAs) on coral reefs has increased considerably in recent decades. Coincident with accelerating degradation of coral reefs, expectations of the benefits that NTAs can provide for coastal societies and sustainability of marine ecosystems has grown. These include increasing abundance of reef organisms both inside and outside NTAs, protecting key ecosystem functions, and providing social and economic benefits through improved fisheries and tourism. However, there is a lack of convincing evidence for many of these expectations. This is the first attempt to synthesize all potential costs and benefits of coral reef NTAs and critically examine evidence of their impacts on both ecosystems and societies. NTAs with high compliance consistently increase the diversity, density and biomass of exploited reef fishes and certain groups of motile invertebrates within their boundaries and have benefits for reef-associated tourism. Some NTAs provide small increases in the abundance of corals and decreases in macroalgal cover. The effects of NTAs on genetic diversity and connectivity among meta-populations are variable or as yet unquantified. There is limited evidence of NTAs providing social benefits through increased fishery yields and tourism revenue. There are examples of both positive and negative effects on social well-being. Finally, sharks, marine megafauna and microbial communities showed few tangible benefits from NTAs. Substantial gaps in the science of coral reef NTAs remain, especially in their capacity to provide socioeconomic benefits. A crucial research priority is understanding how the cumulative effects of climate change will influence the various benefits that NTAs provide. To be effective, NTAs must be used in conjunction with a range of other management tools and applied according to local environmental and societal contexts.
- Mumby, P.J., Elliott, I.A., Eakin, C.M., Skirving, W., Paris, C.B., Edwards, H.J., Enriquez, S., Iglesias-Prieto, R., Cherubin, L.M., and Stevens, J.R. Reserve design for uncertain responses of coral reefs to climate change. Ecology Letters 14(2): 132-140, 2011.
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Rising sea temperatures cause mass coral bleaching and threaten reefs worldwide. We show how maps of variations in thermal stress can be used to help manage reefs for climate change. We map proxies of chronic and acute thermal stress and develop evidence-based hypotheses for the future response of corals to each stress regime. We then incorporate spatially realistic predictions of larval connectivity among reefs of the Bahamas and apply novel reserve design algorithms to create reserve networks for a changing climate. We show that scales of larval dispersal are large enough to connect reefs from desirable thermal stress regimes into a reserve network. Critically, we find that reserve designs differ according to the anticipated scope for phenotypic and genetic adaptation in corals, which remains uncertain. Attempts to provide a complete reserve design that hedged against different evolutionary outcomes achieved limited success, which emphasises the importance of considering the scope for adaptation explicitly. Nonetheless, 15% of reserve locations were selected under all evolutionary scenarios, making them a high priority for early designation. Our approach allows new insights into coral holobiont adaptation to be integrated directly into an adaptive approach to management.
- Edwards, H.J., Elliott, I.A., Eakin, C.M., Irikawa, A., Madin, J.S., McField, M., Morgan, J.A., van Woesik, R., and Mumby, P.J. How much time can herbivore protection buy for coral reefs under realistic regimes of hurricanes and coral bleaching? Global Change Biology 17(6): 2033-2048, 2011.
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Coral reefs have been more severely impacted by recent climate instability than any other ecosystem on Earth. Corals tolerate a narrow range of physical environmental stress, and increases in sea temperature of just 1 ºC over several weeks can result in mass coral mortality, often exceeding 95% of individuals over hundreds of square kilometres. Even conservative climate models predict that mass coral bleaching events could occur annually by 2050. Unfortunately, managers of coral-reef resources have few options available to meet this challenge. Here, we investigate the role that fisheries conservation tools, including the designation of marine reserves, can play in altering future trajectories of Caribbean coral reefs. We use an individual-based model of the ecological dynamics to test the influence of spatially realistic regimes of disturbance on coral populations. Two major sources of disturbance, hurricanes and coral bleaching, are simulated in contrasting regions of the Caribbean: Belize, Bonaire, and the Bahamas. Simulations are extended to 2099 using the HadGEM1 climate model. We find that coral populations can maintain themselves under all levels of hurricane disturbance providing that grazing levels are high. Regional differences in hurricane frequency are found to cause strikingly different spatial patterns of reef health with greater patchiness occurring in Belize, which has less frequent disturbance, than the Bahamas. The addition of coral bleaching led to a much more homogenous reef state over the seascape. Moreover, in the presence of bleaching, all reefs exhibited a decline in health over time, though with substantial variation among regions. Although the protection of herbivores does not prevent reef degradation it does delay rates of coral loss even under the most severe thermal and hurricane regimes. Thus, we can estimate the degree to which local conservation can help buy time for reefs with values ranging between 18 years in the Bahamas and over 50 years in Bonaire, compared with heavily fished systems. Ultimately, we demonstrate that local conservation measures can benefit reef ecosystem services but that their impact will vary spatially and temporally. Recognizing where such management interventions will either help or fail is an important step towards both achieving sustainable use of coral-reef resources and maximizing resource management investments.
- Muñoz, P.D. and Sayago-Gil, M. An overview of cold-water coral protection on the high seas: The Hatton Bank (NE Atlantic) – A case study. Marine Policy 35(5): 615-622, 2011.
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The present paper provides an overview of cold-water corals protection in the Hatton Bank deep-water fisheries through the implementation of the United Nations General Assembly resolution 61/105. The methodology and scientific evidence used to propose protection of cold-water coral ecosystems in the high seas (~16,000 km²) are briefly summarised. The role of international agents and importance of interdisciplinary research for making management decisions are furthermore described. Implementation was slow because (i) of scarce initial scientific knowledge, (ii) research on the high seas was difficult and expensive, (iii) there were several international interests at stake, (iv) agreement from a number of agents was needed, and (v) international advisory and decision making processes were quite slow. Some lessons learned are also discussed since these may help to increase protection efficiency of deep-sea vulnerable marine ecosystems in the high seas.
- Maina, J., McClanahan, T.R., Venus, V., Ateweberhan, M., and Madin, J. Global gradients of coral exposure to environmental stresses and implications for local management. PLoS ONE 6(8): art. e23064, 2011.
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Background The decline of coral reefs globally underscores the need for a spatial assessment of their exposure to multiple environmental stressors to estimate vulnerability and evaluate potential counter-measures. Methodology/Principal Findings This study combined global spatial gradients of coral exposure to radiation stress factors (temperature, UV light and doldrums), stress-reinforcing factors (sedimentation and eutrophication), and stress-reducing factors (temperature variability and tidal amplitude) to produce a global map of coral exposure and identify areas where exposure depends on factors that can be locally managed. A systems analytical approach was used to define interactions between radiation stress variables, stress reinforcing variables and stress reducing variables. Fuzzy logic and spatial ordinations were employed to quantify coral exposure to these stressors. Globally, corals are exposed to radiation and reinforcing stress, albeit with high spatial variability within regions. Based on ordination of exposure grades, regions group into two clusters. The first cluster was composed of severely exposed regions with high radiation and low reducing stress scores (South East Asia, Micronesia, Eastern Pacific and the central Indian Ocean) or alternatively high reinforcing stress scores (the Middle East and the Western Australia). The second cluster was composed of moderately to highly exposed regions with moderate to high scores in both radiation and reducing factors (Caribbean, Great Barrier Reef (GBR), Central Pacific, Polynesia and the western Indian Ocean) where the GBR was strongly associated with reinforcing stress. Conclusions/Significance Despite radiation stress being the most dominant stressor, the exposure of coral reefs could be reduced by locally managing chronic human impacts that act to reinforce radiation stress. Future research and management efforts should focus on incorporating the factors that mitigate the effect of coral stressors until long-term carbon reductions are achieved through global negotiations.
- Pandolfi, J.M., Connolly, S.R., Marshall, D.J., and Cohen, A.L. Projecting coral reef futures under global warming and ocean acidification. Science 333(6041): 418-422, 2011.
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Many physiological responses in present-day coral reefs to climate change are interpreted as consistent with the imminent disappearance of modern reefs globally because of annual mass bleaching events, carbonate dissolution, and insufficient time for substantial evolutionary responses. Emerging evidence for variability in the coral calcification response to acidification, geographical variation in bleaching susceptibility and recovery, responses to past climate change, and potential rates of adaptation to rapid warming supports an alternative scenario in which reef degradation occurs with greater temporal and spatial heterogeneity than current projections suggest. Reducing uncertainty in projecting coral reef futures requires improved understanding of past responses to rapid climate change; physiological responses to interacting factors, such as temperature, acidification, and nutrients; and the costs and constraints imposed by acclimation and adaptation.
- Anthony, K.R.N., Maynard, J.A., Diaz-Pulido, G., Mumby, P.J., Marshall, P.A., Cao, L., and Hoegh-Guldberg, O. Ocean acidification and warming will lower coral reef resilience. Global Change Biology 17(5): 1798-1808, 2011.
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Ocean warming and acidification from increasing levels of atmospheric CO2 represent major global threats to coral reefs, and are in many regions exacerbated by local-scale disturbances such as overfishing and nutrient enrichment. Our understanding of global threats and local-scale disturbances on reefs is growing, but their relative contribution to reef resilience and vulnerability in the future is unclear. Here, we analyse quantitatively how different combinations of CO2 and fishing pressure on herbivores will affect the ecological resilience of a simplified benthic reef community, as defined by its capacity to maintain and recover to coral-dominated states. We use a dynamic community model integrated with the growth and mortality responses for branching corals (Acropora) and fleshy macroalgae (Lobophora). We operationalize the resilience framework by parameterizing the response function for coral growth (calcification) by ocean acidification and warming, coral bleaching and mortality by warming, macroalgal mortality by herbivore grazing and macroalgal growth via nutrient loading. The model was run for changes in sea surface temperature and water chemistry predicted by the rise in atmospheric CO2 projected from the IPCC's fossil-fuel intensive A1FI scenario during this century. Results demonstrated that severe acidification and warming alone can lower reef resilience (via impairment of coral growth and increased coral mortality) even under high grazing intensity and low nutrients. Further, the threshold at which herbivore overfishing (reduced grazing) leads to a coral-algal phase shift was lowered by acidification and warming. These analyses support two important conclusions: Firstly, reefs already subjected to herbivore overfishing and nutrification are likely to be more vulnerable to increasing CO2. Secondly, under CO2 regimes above 450-500 ppm, management of local-scale disturbances will become critical to keeping reefs within an Acropora-rich domain.
- Wild, C., Hoegh-Guldberg, O., Naumann, M.S., Colombo-Pallotta, M.F., Ateweberhan, M., Fitt, W.K., Iglesias-Prieto, R., Palmer, C., Bythell, J.C., Ortiz, J.C., Loya, Y., and van Woesik, R. Climate change impedes scleractinian corals as primary reef ecosystem engineers. Marine and Freshwater Research 62(2): 205-215, 2011.
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Coral reefs are among the most diverse and productive ecosystems on our planet. Scleractinian corals function as the primary reef ecosystem engineers, constructing the framework that serves as a habitat for all other coral reef-associated organisms. However, the coral's engineering role is particularly susceptible to global climate change. Ocean warming can cause extensive mass coral bleaching, which triggers dysfunction of major engineering processes. Sub-lethal bleaching results in the reduction of both primary productivity and coral calcification. This may lead to changes in the release of organic and inorganic products, thereby altering critical biogeochemical and recycling processes in reef ecosystems. Thermal stress-induced bleaching and subsequent coral mortality, along with ocean acidification, further lead to long-term shifts in benthic community structure, changes in topographic reef complexity, and the modification of reef functioning. Such shifts may cause negative feedback loops and further modification of coral-derived inorganic and organic products. This review emphasises the critical role of scleractinian corals as reef ecosystem engineers and highlights the control of corals over key reef ecosystem goods and services, including high biodiversity, coastal protection, fishing, and tourism. Thus, climate change by impeding coral ecosystem engineers will impair the ecosystem functioning of entire reefs.
- Hoegh-Guldberg, O. Coral reef ecosystems and anthropogenic climate change. Regional Environmental Change 11(S1): S215-S227, 2011.
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Coral reef ecosystems are among the most biologically diverse ecosystems on the planet. In addition to their value in terms of biodiversity, coral reefs provide food and resources for over 500 million people. Despite their importance, coral reefs are declining at a rapid rate (1-2% per year) as a result of a range of local (e.g., overexploitation of fisheries, declining water quality) and global (e.g., global warming and ocean acidification) drivers. Extensive experimental and field evidence suggests that atmospheric carbon dioxide concentrations of 450 ppm will lead to the loss of coral-dominated reef systems, with the prospect that dangerous levels of atmospheric carbon dioxide for coral reefs were exceeded in 1979 when mass coral bleaching was reported for the first time. The exact response of coral reefs remains uncertain although it is highly unlikely that coral-dominated reef systems will be present in future oceans at the current rate of warming and acidification of the world's tropical oceans. The loss of these important coastal ecosystems will diminish the resources available to hundreds of millions of people along tropical coastlines. Understanding the impacts on people and industry is an imperative if we are to devise effective systems by which tropical coastal communities are to adapt to rapidly changing tropical coastal environments. Our current understanding of these important issues, however, is in a relatively undeveloped state and must be a priority of future research.
- Yamano, H., Sugihara, K., and Nomura, K. Rapid poleward range expansion of tropical reef corals in response to rising sea surface temperatures. Geophysical Research Letters 38(4): art. L04601, 2011.
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Rising temperatures caused by climatic warming may cause poleward range shifts and/or expansions in species distribution. Tropical reef corals (hereafter corals) are some of the world's most important species, being not only primary producers, but also habitat-forming species, and thus fundamental ecosystem modification is expected according to changes in their distribution. Although most studies of climate change effects on corals have focused on temperature-induced coral bleaching in tropical areas, poleward range shifts and/or expansions may also occur in temperate areas. We show the first large-scale evidence of the poleward range expansion of modern corals, based on 80 years of national records from the temperate areas of Japan, where century-long measurements of in situ sea-surface temperatures have shown statistically significant rises. Four major coral species categories, including two key species for reef formation in tropical areas, showed poleward range expansions since the 1930s, whereas no species demonstrated southward range shrinkage or local extinction. The speed of these expansions reached up to 14 km/year, which is far greater than that for other species. Our results, in combination with recent findings suggesting range expansions of tropical coral-reef associated organisms, strongly suggest that rapid, fundamental modifications of temperate coastal ecosystems could be in progress.
- Burt, J., Al Harthi, S., and Al Cibahy, A. Long-term impacts of coral bleaching events on the world's warmest reefs. Marine Environmental Research 72(4): 225-229, 2011.
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The southern Arabian Gulf houses some of the most thermally tolerant corals on earth, but severe bleaching in the late 1990s caused widespread mortality. More than a decade later, corals still dominated benthos (mean: 40 ± 3% cover on 10 sites spanning >350 km; range: 11.0–65.6%), but coral communities varied spatially. Sites to the west generally had low species richness and coral cover (mean: 3.2 species per transect, 31% cover), with Porites dominated communities (88% of coral) that are distinct from more diverse and higher cover eastern sites (mean: 10.3 species per transect, 62% cover). These patterns reflect both the more extreme bleaching to the west in the late 1990s as well as the higher faviid dominated recruitment to the east in subsequent years. There has been limited recovery of the formerly dominant Acropora, which now represents <1% of the benthos, likely as a result of recruitment failure. Results indicate that severe bleaching can have substantial long-term impacts on coral communities, even in areas with corals tolerant to environmental extremes.
- Nakamura, M., Ohki, S., Suzuki, A., and Sakai, K. Coral larvae under ocean acidification: Survival, metabolism, and metamorphosis. PLoS ONE 6(1): art. e14521, 2011.
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Ocean acidification may negatively impact the early life stages of some marine invertebrates including corals. Although reduced growth of juvenile corals in acidified seawater has been reported, coral larvae have been reported to demonstrate some level of tolerance to reduced pH. We hypothesize that the observed tolerance of coral larvae to low pH may be partly explained by reduced metabolic rates in acidified seawater because both calcifying and non-calcifying marine invertebrates could show metabolic depression under reduced pH in order to enhance their survival. In this study, after 3-d and 7-d exposure to three different pH levels (8.0, 7.6, and 7.3), we found that the oxygen consumption of Acropora digitifera larvae tended to be suppressed with reduced pH, although a statistically significant difference was not observed between pH conditions. Larval metamorphosis was also observed, confirming that successful recruitment is impaired when metamorphosis is disrupted, despite larval survival. Results also showed that the metamorphosis rate significantly decreased under acidified seawater conditions after both short (2 h) and long (7 d) term exposure. These results imply that acidified seawater impacts larval physiology, suggesting that suppressed metabolism and metamorphosis may alter the dispersal potential of larvae and subsequently reduce the resilience of coral communities in the near future as the ocean pH decreases.
- Albright, R. Reviewing the effects of ocean acidification on sexual reproduction and early life history stages of reef-building corals. Journal of Marine Biology 2011: art. 473615, 2011.
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Ocean acidification (OA) is a relatively young yet rapidly developing scientific field. Assessing the potential response(s) of marine organisms to projected near-future OA scenarios has been at the forefront of scientific research, with a focus on ecosystems (e.g., coral reefs) and processes (e.g., calcification) that are deemed particularly vulnerable. Recently, a heightened emphasis has been placed on evaluating early life history stages as these stages are generally perceived to be more sensitive to environmental change. The number of acidification-related studies focused on early life stages has risen dramatically over the last several years. While early life history stages of corals have been understudied compared to other marine invertebrate taxa (e.g., echinoderms, mollusks), numerous studies exist to contribute to our status of knowledge regarding the potential impacts of OA on coral recruitment dynamics. To synthesize this information, the present paper reviews the primary literature on the effects of acidification on sexual reproduction and early stages of corals, incorporating lessons learned from more thoroughly studied taxa to both assess our current understanding of the potential impacts of OA on coral recruitment and to inform and guide future research in this area.
- Santos, I.R., Glud, R.N., Maher, D., Erler, D., and Eyre, B.D. Diel coral reef acidification driven by porewater advection in permeable carbonate sands, Heron Island, Great Barrier Reef. Geophysical Research Letters 38(3): art. 3604, 2011.
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Little is known about how biogeochemical processes in permeable sediments affect the pH of coastal waters. We demonstrate that seawater recirculation in permeable sands can play a major role in proton (H+) cycling in a coral reef lagoon. The diel pH range (up to 0.75 units) in the Heron Island lagoon was the broadest ever reported for reef waters, and the night-time pH (7.69) was comparable to worst-case scenario predictions for seawater pH in 2100. The net contribution of coarse carbonate sands to the whole system H+ fluxes was only 9% during the day, but approached 100% at night when small scale (i.e., flow and topography-induced pressure gradients) and large scale (i.e., tidal pumping as traced by radon) seawater recirculation processes were synergistic. Reef lagoon sands were a net sink for H+, and the sink strength was a function of porewater flushing rate. Our observations suggest that the metabolism of advection-dominated carbonate sands may provide a currently unknown feedback to ocean acidification.
- Kleypas, J.A., Anthony, K.R.N., and Gattuso, J.-P. Coral reefs modify their seawater carbon chemistry – case study from a barrier reef (Moorea, French Polynesia). Global Change Biology 17(12): 3667-3678, 2011.
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Changes in the carbonate chemistry of coral reef waters are driven by carbon fluxes from two sources: concentrations of CO2 in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air-sea flux of CO2 driven by benthic community processes can exceed that due to increases in atmospheric CO2 (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae, and sand. Building on data from previous carbon flux studies along a reef-flat transect in Moorea (French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon (CT) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity (AT) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Ωa). We use the model to test how changes in atmospheric CO2 forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream-downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies.
- Albright, R. and Langdon, C. Ocean acidification impacts multiple early life history processes of the Caribbean coral Porites astreoides. Global Change Biology 17(7): 2478-2487, 2011.
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Ocean acidification (OA) refers to the increase in acidity (decrease in pH) of the ocean's surface waters resulting from oceanic uptake of atmospheric carbon dioxide (CO2). Mounting experimental evidence suggests that OA threatens numerous marine organisms, including reef-building corals. Coral recruitment is critical to the persistence and resilience of coral reefs and is regulated by several early life processes, including: larval availability (gamete production, fertilization, etc.), larval settlement, postsettlement growth, and survival. Environmental factors that disrupt these early life processes can result in compromised or failed recruitment and profoundly affect future population dynamics. To evaluate the effects of OA on the sexual recruitment of corals, we tested larval metabolism, larval settlement, and postsettlement growth of the common Caribbean coral Porites astreoides at three pCO2 levels: ambient seawater (380 μatm) and two pCO2 scenarios that are projected to occur by the middle (560 μatm) and end (800 μatm) of the century. Our results show that larval metabolism is depressed by 27% and 63% at 560 and 800 μatm, respectively, compared with controls. Settlement was reduced by 42-45% at 560 μatm and 55-60% at 800 μatm, relative to controls. Results indicate that OA primarily affects settlement via indirect pathways, whereby acidified seawater alters the substrate community composition, limiting the availability of settlement cues. Postsettlement growth decreased by 16% and 35% at 560 and 800 μatm, respectively, relative to controls. This study demonstrates that OA has the potential to negatively impact multiple early life history processes of P. astreoides and may contribute to substantial declines in sexual recruitment that are felt at the community and/or ecosystem scale.
- Purkis, S.J., Renegar, D.A., and Riegl, B.M. The most temperature-adapted corals have an Achilles' Heel. Marine Pollution Bulletin 62(2): 246-250, 2011.
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The corals of the Persian/Arabian Gulf are better adapted to temperature fluctuations than elsewhere in the Indo-Pacific. The Gulf is an extreme marine environment displaying the highest known summer water temperatures for any reef area. The small and shallow sea can be considered a good analogue to future conditions for the rest of the world's oceans under global warming. The fact that corals can persist in such a demanding environment indicates that they have been able to acclimatize and selectively adapt to elevated temperature. The implication being that colonies elsewhere may be able to follow suit. This in turn provides hope that corals may, given sufficient time, similarly adapt to survive even in an impoverished form, under conditions of acidification-driven lowering of CaCO3 saturation state, a further consequence of raised atmospheric CO2. This paper demonstrates, however, that the uniquely adapted corals of the Gulf may, within the next three centuries, be threatened by a chronic habitat shortage brought about by the dissolution of the lithified seabed on which they rely for colonisation. This will occur due to modifications in the chemical composition of the Gulf waters due to climate change.
- Veron, J.E.N. Ocean acidification and coral reefs: An emerging big picture. Diversity 3(2): 262-274, 2011.
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This article summarises the sometimes controversial contributions made by the different sciences to predict the path of ocean acidification impacts on the diversity of coral reefs during the present century. Although the seawater carbonate system has been known for a long time, the understanding of acidification impacts on marine biota is in its infancy. Most publications about ocean acidification are less than a decade old and over half are about coral reefs. Contributions from physiological studies, particularly of coral calcification, have covered such a wide spectrum of variables that no cohesive picture of the mechanisms involved has yet emerged. To date, these studies show that coral calcification varies with carbonate ion availability which, in turn controls aragonite saturation. They also reveal synergies between acidification and the better understood role of elevated temperature. Ecological studies are unlikely to reveal much detail except for the observations of the effects of carbon dioxide springs in reefs. Although ocean acidification events are not well constrained in the geological record, recent studies show that they are clearly linked to extinction events including four of the five greatest crises in the history of coral reefs. However, as ocean acidification is now occurring faster than at any know time in the past, future predictions based on past events are in unchartered waters. Pooled evidence to date indicates that ocean acidification will be severely affecting reefs by mid century and will have reduced them to ecologically collapsed carbonate platforms by the century's end. This review concludes that most impacts will be synergistic and that the primary outcome will be a progressive reduction of species diversity correlated with habitat loss and widespread extinctions in most metazoan phyla.
- Fabricius, K.E., Langdon, C., Uthicke, S., Humphrey, C., Noonan, S., De'ath, G., Okazaki, R., Muehllehner, N., Glas, M.S., and Lough, J.M. Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate Change 1(3): 165-169, 2011.
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Experiments have shown that ocean acidification due to rising atmospheric carbon dioxide concentrations has deleterious effects on the performance of many marine organisms. However, few empirical or modelling studies have addressed the long-term consequences of ocean acidification for marine ecosystems. Here we show that as pH declines from 8.1 to 7.8 (the change expected if atmospheric carbon dioxide concentrations increase from 390 to 750 ppm, consistent with some scenarios for the end of this century) some organisms benefit, but many more lose out. We investigated coral reefs, seagrasses and sediments that are acclimatized to low pH at three cool and shallow volcanic carbon dioxide seeps in Papua New Guinea. At reduced pH, we observed reductions in coral diversity, recruitment and abundances of structurally complex framework builders, and shifts in competitive interactions between taxa. However, coral cover remained constant between pH 8.1 and ~7:8, because massive Porites corals established dominance over structural corals, despite low rates of calcification. Reef development ceased below pH 7.7. Our empirical data from this unique field setting confirm model predictions that ocean acidification, together with temperature stress, will probably lead to severely reduced diversity, structural complexity and resilience of Indo-Pacific coral reefs within this century.
- Rodolfo-Metalpa, R., Houlbrèque, F., Tambutté, É., Boisson, F., Baggini, C., Patti, F.P., Jeffree, R., Fine, M., Foggo, A., Gattuso, J.-P., and Hall-Spencer, J.M. Coral and mollusc resistance to ocean acidification adversely affected by warming. Nature Climate Change 1(6): 308-312, 2011.
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Increasing atmospheric carbon dioxide (CO2) concentrations are expected to decrease surface ocean pH by 0.3-0.5 units by 2100, lowering the carbonate ion concentration of surface waters. This rapid acidification is predicted to dramatically decrease calcification in many marine organisms. Reduced skeletal growth under increased CO2 levels has already been shown for corals, molluscs and many other marine organisms. The impact of acidification on the ability of individual species to calcify has remained elusive, however, as measuring net calcification fails to disentangle the relative contributions of gross calcification and dissolution rates on growth. Here, we show that corals and molluscs transplanted along gradients of carbonate saturation state at Mediterranean CO2 vents are able to calcify and grow at even faster than normal rates when exposed to the high CO2 levels projected for the next 300 years. Calcifiers remain at risk, however, owing to the dissolution of exposed shells and skeletons that occurs as pH levels fall. Our results show that tissues and external organic layers play a major role in protecting shells and skeletons from corrosive sea water, limiting dissolution and allowing organisms to calcify. Our combined field and laboratory results demonstrate that the adverse effects of global warming are exacerbated when high temperatures coincide with acidification.
- Diaz-Pulido, G., Gouezo, M., Tilbrook, B., Dove, S., and Anthony, K.R.N. High CO2 enhances the competitive strength of seaweeds over corals. Ecology Letters 14(2): 156-162, 2011.
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Space competition between corals and seaweeds is an important ecological process underlying coral-reef dynamics. Processes promoting seaweed growth and survival, such as herbivore overfishing and eutrophication, can lead to local reef degradation. Here, we present the case that increasing concentrations of atmospheric CO2 may be an additional process driving a shift from corals to seaweeds on reefs. Coral (Acropora intermedia) mortality in contact with a common coral-reef seaweed (Lobophora papenfussii) increased two- to threefold between background CO2 (400 ppm) and highest level projected for late 21st century (1140 ppm). The strong interaction between CO2 and seaweeds on coral mortality was most likely attributable to a chemical competitive mechanism, as control corals with algal mimics showed no mortality. Our results suggest that coral (Acropora) reefs may become increasingly susceptible to seaweed proliferation under ocean acidification, and processes regulating algal abundance (e.g. herbivory) will play an increasingly important role in maintaining coral abundance.
- de Putron, S.J., McCorkle, D.C., Cohen, A.L., and Dillon, A.B. The impact of seawater saturation state and bicarbonate ion concentration on calcification by new recruits of two Atlantic corals. Coral Reefs 30(2): 321-328, 2011.
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Rising concentrations of atmospheric CO2 are changing the carbonate chemistry of the oceans, a process known as ocean acidification (OA). Absorption of this CO2 by the surface oceans is increasing the amount of total dissolved inorganic carbon (DIC) and bicarbonate ion (HCO3−) available for marine calcification yet is simultaneously lowering the seawater pH and carbonate ion concentration ([CO32−]), and thus the saturation state of seawater with respect to aragonite (Ωar). We investigated the relative importance of [HCO3−] versus [CO32−] for early calcification by new recruits (primary polyps settled from zooxanthellate larvae) of two tropical coral species, Favia fragum and Porites astreoides. The polyps were reared over a range of Ωar values, which were manipulated by both acid-addition at constant pCO2 (decreased total [HCO3−] and [CO32−]) and by pCO2 elevation at constant alkalinity (increased [HCO3−], decreased [CO32−]). Calcification after 2weeks was quantified by weighing the complete skeleton (corallite) accreted by each polyp over the course of the experiment. Both species exhibited the same negative response to decreasing [CO32−] whether Ωar was lowered by acid-addition or by pCO2 elevation –calcification did not follow total DIC or [HCO3−]. Nevertheless, the calcification response to decreasing [CO32−] was nonlinear. A statistically significant decrease in calcification was only detected between Ωar=<2.5 and Ωar=1.1–1.5, where calcification of new recruits was reduced by 22–37% per 1.0 decrease in Ωar. Our results differ from many previous studies that report a linear coral calcification response to OA, and from those showing that calcification increases with increasing [HCO3−]. Clearly, the coral calcification response to OA is variable and complex. A deeper understanding of the biomineralization mechanisms and environmental conditions underlying these variable responses is needed to support informed predictions about future OA impacts on corals and coral reefs.
- Kemp, D.W., Oakley, C.A., Thornhill, D.J., Newcomb, L.A., Schmidt, G.W., and Fitt, W.K. Catastrophic mortality on inshore coral reefs of the Florida Keys due to severe low-temperature stress. Global Change Biology 17(11): 3468-3477, 2011.
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Coral reefs of the Florida Keys typically experience seasonal temperatures of 20–31 °C. Deviation outside this range causes physiological impairment of reef-building corals, potentially leading to coral colony death. In January and February 2010, two closely spaced cold fronts, possibly driven by an unusually extreme Arctic Oscillation, caused sudden and severe seawater temperature declines in the Florida Keys. Inshore coral reefs [e.g., Admiral Reef (ADM)] experienced lower sustained temperatures (i.e., <12 °C) than those further offshore [e.g., Little Grecian Reef (LG), minimum temperature = 17.2 °C]. During February and March 2010, we surveyed ADM and observed a mass die-off of reef-building corals, whereas 12 km away LG did not exhibit coral mortality. We subsequently measured the physiological effects of low-temperature stress on three common reef-building corals (i.e., Montastraea faveolata, Porites astreoides, and Siderastrea siderea) over a range of temperatures that replicated the inshore cold-water anomaly (i.e., from 20 to 16 to 12 °C and back to 20 °C). Throughout the temperature modulations, coral respiration as well as endosymbiont gross photosynthesis and maximum quantum efficiency of photosystem II were measured. In addition, Symbiodinium genotypic identity, cell densities, and chlorophyll a content were determined at the beginning and conclusion of the experiment. All corals were significantly affected at 12 °C, but species-specific physiological responses were found indicating different coral and/or Symbiodinium cold tolerances. Montastraea faveolata and P. astreoides appeared to be most negatively impacted because, upon return to 20 °C, significant reductions in gross photosynthesis and dark respiration persisted. Siderastrea siderea, however, readily recovered to pre-treatment rates of dark respiration and gross photosynthesis. Visual surveys of inshore reefs corroborated these results, with S. siderea being minimally affected by the cold-water anomaly, whereas M. faveolata and P. astreoides exhibited nearly 100% mortality. This study highlights the importance of understanding the physiological attributes of genotypically distinct coral-Symbiodinium symbioses that contribute to tolerance, recovery, and consequences to an environmental perturbation. These data also document effects of a rarely studied environmental stressor, possibly initiated by remote global climate events, on coral-Symbiodinium symbioses and coral reef communities.
- Vermeij, M.J.A., van Moorselaar, I., Engelhard, S., Hörnlein, C., Vonk, S.M., and Visser, P.M. The effects of nutrient enrichment and herbivore abundance on the ability of turf algae to overgrow coral in the Caribbean. PLoS ONE 5(12): art. e14312, 2010.
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Turf algae are multispecies communities of small marine macrophytes that are becoming a dominant component of coral reef communities around the world. To assess the impact of turf algae on corals, we investigated the effects of increased nutrients (eutrophication) on the interaction between the Caribbean coral Montastraea annularis and turf algae at their growth boundary. We also assessed whether herbivores are capable of reducing the abundance of turf algae at coral-algae boundaries. We found that turf algae cause visible (overgrowth) and invisible negative effects (reduced fitness) on neighbouring corals. Corals can overgrow neighbouring turf algae very slowly (at a rate of 0.12 mm 3 wk-1) at ambient nutrient concentrations, but turf algae overgrew corals (at a rate of 0.34 mm 3 wk-1) when nutrients were experimentally increased. Exclusion of herbivores had no measurable effect on the rate turf algae overgrew corals. We also used PAM fluorometry (a common approach for measuring of a colony's "fitness") to detect the effects of turf algae on the photophysiology of neighboring corals. Turf algae always reduced the effective photochemical efficiency of neighbouring corals, regardless of nutrient and/or herbivore conditions. The findings that herbivores are not capable of controlling the abundance of turf algae and that nutrient enrichment gives turf algae an overall competitive advantage over corals together have serious implications for the health of Caribbean coral reef systems. At ambient nutrient levels, traditional conservation measures aimed at reversing coral-to-algae phase shifts by reducing algal abundance (i.e., increasing herbivore populations by establishing Marine Protected Areas or tightening fishing regulations) will not necessarily reduce the negative impact of turf algae on local coral communities. Because turf algae have become the most abundant benthic group on Curaçao (and likely elsewhere in the Caribbean), new conservation strategies are required to mitigate their negative impact on coral communities.
- Juhasz, A., Ho, E., Bender, E., and Fong, P. Does use of tropical beaches by tourists and island residents result in damage to fringing coral reefs? A case study in Moorea French Polynesia. Marine Pollution Bulletin 60(12): 2251-2256, 2010.
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Although coral reefs worldwide are subject to increasing global threats, humans also impact coral reefs directly through localized activities such as snorkeling, kayaking and fishing. We investigated five sites on the northern shore of Moorea, French Polynesia, and quantified the number of visitors on the beach and in shallow water. In field surveys, we measured total coral cover and colony sizes of two common genera, Porites and Acropora, a massive and branching morphology, respectively. One site, which hosted over an order of magnitude more people than the other four, had significantly less total coral cover and supported very little branching Acropora. In addition, size frequency distributions of both the branching and massive genera were skewed toward smaller colony sizes at the high use site. Our results demonstrated that the use of tropical beaches may result in less coral cover, with branching colonies rare and small.
- Futch, J.C., Griffin, D.W., Banks, K., and Lipp, E.K. Evaluation of sewage source and fate on southeast Florida coastal reefs. Marine Pollution Bulletin 62(11): 2308-2316, 2011.
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Water, sponge and coral samples were collected from stations impacted by a variety of pollution sources and screened for human enteric viruses as conservative markers for human sewage. While human enteroviruses and adenoviruses were not detected, noroviruses (NoV; human genogroups I and II) were detected in 31% of samples (especially in sponge tissue). Stations near inlets were the only ones to show multiple sample types positive for NoV. Fecal indicator bacteria and enteric viruses were further evaluated at multiple inlet stations on an outgoing tide. Greatest indicator concentrations and highest prevalence of viruses were found at the mouth of the inlet and offshore in the inlet plume. Results suggest that inlets moving large volumes of water into the coastal zone with tides may be an important source of fecal contaminants. Efforts to reduce run-off or unintended release of water into the Intracoastal Waterway may lower contaminants entering sensitive coastal areas.
- Jones, R.J. Environmental effects of the cruise tourism boom: Sediment resuspension from cruise ships and the possible effects of increased turbidity and sediment deposition on corals (Bermuda). Bulletin of Marine Science 87(3): 659-679, 2011.
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In the wider Caribbean, the cruise tourism boom is causing a transition from land-based (hotel) to ship-based (cruise ship) tourism. Associated with this boom has been an increase in the size of the cruise ships, with many now being Panamax/post-Panamax "mega" cruise ships. The social/environmental consequences of these changes are likely to be profound, but are also likely to be country-specific. In Bermuda, mega cruise ships can resuspend large amounts of sediment that drift onto nearby reefs. Data were compiled on cruise ship sizes and speeds entering and leaving two ports in Bermuda. In situ data were collected from multiple sites using a turbidity sensor, arrays of sediment traps, and water sample analysis. Turbidity levels in the plumes can reach 50 NTU (80 mg l-1), but rapidly decrease to background levels (<1 NTU) over ~4-6 hrs. Particle size analysis revealed the plumes are composed of very fine sediments, with a median diam of <5 μm (max <200 μm). Sediment trap accumulation rates were found to be highest beside the shipping channels (up to ~5 mg cm-2 d-1) and decrease to background rates (1-2 mg cm-2 d-1) within a few hundred meters of the channels. These levels were significantly higher than the naturally very low levels within the lagoon. Based on existing literature, the intensity/duration/frequency of sediment exposure were considered unlikely to result in discernible physiological impacts on adult corals in the short term. However, long-term effects on juvenile coral survival and settlement success (i.e., at the population/community level) could not be discounted. Since sediment resuspension was found to be related to cruise ship speed, remedial action should involve reducing ships' speed to <18.5-22 km hr-1 (or 10-12 kts) when inside the lagoon.
- Hannak, J.S., Kompatscher, S., Stachowitsch, M., and Herler, J. Snorkelling and trampling in shallow-water fringing reefs: Risk assessment and proposed management strategy. Journal of Environmental Management 92(10): 2723-2733, 2011.
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Shallow reefs (reef flats <1.5m) in the northern Red Sea are impacted by growing tourism that includes swimmers, snorkellers and reef walkers but have largely been neglected in past studies. We selected a fringing reef along the lagoon of Dahab (Sinai, Egypt) as a model for a management strategy. Point-intercept line transects were used to determine substrate composition, coral community and condition, and the coral damage index (CDI) was applied. Approximately 84% of the coral colonies showed signs of damage such as breakage, partial mortality or algal overgrowth, especially affecting the most frequent coral genus Acropora. Questionnaires were used to determine the visitors' socio-economic background and personal attitudes regarding snorkelling, SCUBA-diving and interest in visiting a prospective snorkelling trail. Experiencing nature (97%) was by far the strongest motivation, and interest in further education about reef ecology and skill training was high. Less experienced snorkellers and divers – the target group for further education and skill training – were those most prepared to financially support such a trail. We therefore recommend a guided underwater snorkelling trail and restricting recreational use to a less sensitive 'ecotourism zone' while protecting the shallow reef flat. Artificial structures can complete the trail and offer the opportunity to snorkel over deeper areas at unfavourable tide or wind conditions. This approach provides a strategy for the management and conservation of shallow-water reefs, which are facing increasing human impact here and elsewhere.
- Deidun, A., Tsounis, G., Balzan, F., and Micallef, A. Records of black coral (Antipatharia) and red coral (Corallium rubrum) fishing activities in the Maltese Islands. Marine Biodiversity Records 3: art. e90, 2010.
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This study presents a description of the little known coral fishery activities around the Maltese Islands. Apart from previously unpublished catch data on Corallium rubrum, this study also reveals, sporadic harvesting of black coral (Antipatharia) past and serves as a first record of Leiopathes glaberrima in Maltese waters. The data indicate that precious coral fishing was regulated on an arbitrary license system that was not based on scientific management. Both fisheries ceased in 1987, although personal communication with industry operators indicates that C. rubrum is still being unofficially fished on a reduced scale. As Mediterranean precious coral fisheries originated so long-age, and since so little is known about precious coral species' distribution, the presented historical data may help in evaluating baseline levels of population status and past anthropogenic impact. Finally, the study also highlights the importance of an evaluation of the current population status of precious coral species and a more effective curbing of illegal fishing activities to achieve the desired conservation of the precious coral species in question.
- Fujii, T., Keshavmurthy, S., Zhou, W., Hirose, E., Chen, C.A., and Reimer, J.D. Coral-killing cyanobacteriosponge (Terpios hoshinota) on the Great Barrier Reef. Coral Reefs 30(2): 483, 2011.
- Golbuu, Y., van Woesik, R., Richmond, R.H., Harrison, P., and Fabricius, K.E. River discharge reduces reef coral diversity in Palau. Marine Pollution Bulletin 62(4): 824-831, 2011.
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Coral community structure is often governed by a suite of processes that are becoming increasingly influenced by land-use changes and related terrestrial discharges. We studied sites along a watershed gradient to examine both the physical environment and the associated biological communities. Transplanted corals showed no differences in growth rates and mortality along the watershed gradient. However, coral cover, coral richness, and coral colony density increased with increasing distance from the mouth of the bay. There was a negative relationship between coral cover and mean suspended solids concentration. Negative relationships were also found between terrigenous sedimentation rates and the richness of adult and juvenile corals. These results have major implications not only for Pacific islands but for all countries with reef systems downstream of rivers. Land development very often leads to increases in river runoff and suspended solids concentrations that reduce coral cover and coral diversity on adjacent reefs.
- Hoey, A.S. and Bellwood, D.R. Suppression of herbivory by macroalgal density: a critical feedback on coral reefs? Ecology Letters 14(3): 267-273, 2011.
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Coral reefs globally are in decline, with some reefs undergoing phase shifts from coral-dominance to degraded states dominated by large fleshy macroalgae. These shifts have been underpinned by the overharvesting of herbivorous fishes and represent a fundamental change in the physical structure of these reefs. Although the physical structure provided by corals is regarded as a key feature that facilitates herbivore activity, the influence of the physical structure of macroalgal stands is largely unknown. Using transplanted Sargassum, the largest coral reef macroalga, we created habitat patches of predetermined macroalgal density (0.25-6.23 kg m-2). Remote video cameras revealed both grazing and browsing fishes avoided high density patches, preferring relatively open areas with low macroalgal cover. This behaviour may provide a positive feedback leading to the growth and persistence of macroalgal stands; increasing the stability of phase shifts to macroalgae.
- Paul, V.J., Kuffner, I.B., Walters, L.J., Ritson-Williams, R., Beach, K.S., and Becerro, M.A. Chemically mediated interactions between macroalgae Dictyota spp. and multiple life-history stages of the coral Porites astreoides. Marine Ecology Progress Series 426: 161-170, 2011.
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Competition between corals and macroalgae is often assumed to occur on reefs, especially those that have undergone shifts from coral to algal dominance; however, data examining these competitive interactions, especially during the early life-history stages of corals, are scarce. We conducted a series of field and outdoor seawater-table experiments to test the hypothesis that allelopathy (chemical inhibition) mediates interactions between 2 common brown macroalgae, Dictyota pulchella and D. pinnatifida, and the coral Porites astreoides at different life-history stages of the coral. D. pinnatifida significantly reduced larval survival and larval recruitment. The extracts of both D. pinnatifida and D. pulchella significantly reduced larval survival, and the extract of D. pulchella also negatively influenced larval recruitment. There was no measurable effect of the crude extracts from Dictyota spp. on the photophysiology of adult corals. Our results provide evidence that these Dictyota species chemically compete with P. astreoides by negatively affecting larval settlement and recruitment as well as the survival of larvae and new recruits. Macroalgae may perpetuate their dominance on degraded reefs by chemically inhibiting the process of coral recruitment.
- Lirman, D. et al. Severe 2010 cold-water event caused unprecedented mortality to corals of the Florida Reef Tract and reversed previous survivorship patterns. PLoS ONE 6(8): art. e23047, 2011.
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Background Coral reefs are facing increasing pressure from natural and anthropogenic stressors that have already caused significant worldwide declines. In January 2010, coral reefs of Florida, United States, were impacted by an extreme cold-water anomaly that exposed corals to temperatures well below their reported thresholds (16°C), causing rapid coral mortality unprecedented in spatial extent and severity. Methodology/Principal Findings Reef surveys were conducted from Martin County to the Lower Florida Keys within weeks of the anomaly. The impacts recorded were catastrophic and exceeded those of any previous disturbances in the region. Coral mortality patterns were directly correlated to in-situ and satellite-derived cold-temperature metrics. These impacts rival, in spatial extent and intensity, the impacts of the well-publicized warm-water bleaching events around the globe. The mean percent coral mortality recorded for all species and subregions was 11.5% in the 2010 winter, compared to 0.5% recorded in the previous five summers, including years like 2005 where warm-water bleaching was prevalent. Highest mean mortality (15%-39%) was documented for inshore habitats where temperatures were <11°C for prolonged periods. Increases in mortality from previous years were significant for 21 of 25 coral species, and were 1-2 orders of magnitude higher for most species. Conclusions/Significance The cold-water anomaly of January 2010 caused the worst coral mortality on record for the Florida Reef Tract, highlighting the potential catastrophic impacts that unusual but extreme climatic events can have on the persistence of coral reefs. Moreover, habitats and species most severely affected were those found in high-coral cover, inshore, shallow reef habitats previously considered the "oases" of the region, having escaped declining patterns observed for more offshore habitats. Thus, the 2010 cold-water anomaly not only caused widespread coral mortality but also reversed prior resistance and resilience patterns that will take decades to recover.
- Huete-Stauffer, C., Vielmini, I., Palma, M., Navone, A., Panzalis, P., Vezzulli, L., Misic, C., and Cerrano, C. Paramuricea clavata (Anthozoa, Octocorallia) loss in the Marine Protected Area of Tavolara (Sardinia, Italy) due to a mass mortality event. Marine Ecology: An Evolutionary Perspective 32(S1): 107-116, 2011.
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Recent studies highlight an increase in the frequency and intensity of marine mass mortalities of several species over the past 30-40 years, mainly in tropical and temperate areas. In the Mediterranean Sea these episodes particularly affect benthic suspension feeders, such as sponges and cnidarians. The main objective of this work was to document the loss of one of the main Mediterranean seascapes, Paramuricea clavata forests at the Marine Protected Area of Tavolara Punta Coda Cavallo, Sardinia (Italy), during the summer of 2008. Data regarding colony height, density, level of damage, and microbiological community were collected at two sites. Such parameters help us understand how mass mortality mechanisms act on this ecosystem engineer. We identified a change in size class distribution following a mass mortality that leaves mainly small colonies with a decrease in habitat complexity. Several tests on water chemistry demonstrate that the mortality event was not caused by local contamination. Moreover, microbiological tests on potential pathogenic agents suggest that bacteria belonging to the genus Vibrio are present as an opportunistic and not an etiological cause of P. clavata mortality events. Possible restoration approaches are discussed.
- Alvarez-Filip, L., Coté, I.M., Gill, J.A., Watkinson, A.R., and Dulvy, N.K. Region-wide temporal and spatial variation in Caribbean reef architecture: is coral cover the whole story? Global Change Biology 17(7): 2470-2477, 2011.
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The architectural complexity of coral reefs is largely generated by reef-building corals, yet the effects of current regional-scale declines in coral cover on reef complexity are poorly understood. In particular, both the extent to which declines in coral cover lead to declines in complexity and the length of time it takes for reefs to collapse following coral mortality are unknown. Here we assess the extent of temporal and spatial covariation between coral cover and reef architectural complexity using a Caribbean-wide dataset of temporally replicated estimates spanning four decades. Both coral cover and architectural complexity have declined rapidly over time, with little evidence of a time-lag. However, annual rates of change in coral cover and complexity do not covary, and levels of complexity vary greatly among reefs with similar coral cover. These findings suggest that the stressors influencing Caribbean reefs are sufficiently severe and widespread to produce similar regional-scale declines in coral cover and reef complexity, even though reef architectural complexity is not a direct function of coral cover at local scales. Given that architectural complexity is not a simple function of coral cover, it is important that conservation monitoring and restoration give due consideration to both architecture and coral cover. This will help ensure that the ecosystem services supported by architectural complexity, such as nutrient recycling, dissipation of wave energy, fish production and diversity, are maintained and enhanced.
- Stella, J.S., Pratchett, M.S., Hutchings, P.A., and Jones, G.P. Coral-associated invertebrates: Diversity, ecological importance and vulnerability to disturbance. Oceanography and Marine Biology: An Annual Review (49): 43-116, 2011.
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The biodiversity of coral reefs is dominated by invertebrates. Many of these invertebrates live in close association with scleractinian corals, relying on corals for food, habitat or settlement cues. Given their strong dependence on corals, it is of great concern that our knowledge of coral-associated invertebrates is so limited, especially in light of severe and ongoing degradation of coral reef habitats and the potential for species extinctions. This review examines the taxonomic extent of coral-associated invertebrates, the levels of dependence on coral hosts, the nature of associations between invertebrates and corals, and the factors that threaten coral-associated invertebrates now and in the future. There are at least 860 invertebrate species that have been described as coral associated, of which 310 are decapod crustaceans. Over half of coral-associated invertebrates appear to have an obligate dependence on live corals. Many exhibit a high degree of preference for one or two coral species, with species in the genera Pocillopora, Acropora and Stylophora commonly preferred. This level of habitat specialization may place coral-associated invertebrates at a great risk of extinction, particularly because preferred coral genera are those most susceptible to coral bleaching and mortality. In turn, many corals are also reliant on the services of particular invertebrates, leading to strong feedbacks between abundance of corals and their associated invertebrates. The loss of even a few preferred coral taxa could lead to a substantial decline in invertebrate biodiversity and have far-reaching effects on coral reef ecosystem function. A full appreciation of the consequences of further coral reef degradation for invertebrate biodiversity awaits a more complete description of the diversity of coral-associated invertebrates, the roles they play in coral reef ecosystems, their contribution to reef resilience and their conservation needs.
- Glynn, P.W. In tandem reef coral and cryptic metazoan declines and extinctions. Bulletin of Marine Science 87(4): 767-794, 2011.
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Coral reef degradation and loss have been extensively documented worldwide during the last few decades. While much attention has been directed toward the mortality of reef-building corals vis-à-vis various observed disturbances (e.g., bleaching, diseases, overfishing, nutrification), the fate of other reef-associated metazoans, especially invertebrates, has not received sufficient attention. Living and dead corals, reef frameworks, and carbonate sediments provide essential habitat niches for a multitude of symbiotic and cryptic species. Thirty-one animal phyla contain species that inhabit coral reefs with known global species richness estimated at 93,000. Possibly as many as 1,000,000 reef-associated metazoans occur globally. Many of these species are undiscovered because of their cryptic or sibling nature. Metazoan reef associates have important functional roles on reefs, e.g., increasing survivorship of coral hosts, aiding in reef framework construction (calcification, consolidation), providing trophic resources, affecting coral mortality (corallivores) and erosion (bioerosion). Despite widespread bleaching and mortality, no reef-building corals (Scleractinia) have yet to become globally extinct. Three populations of Millepora spp. (Hydroida) were severely impacted in Pacific Panama during the 1982-83 El Niño-Southern Oscillation event. Present status indicates recovery of Millepora intricata Milne-Edwards and Haime, 1860 to shallow reef zones from relatively deep (10-15 m) refugia. Furthermore, two hydrocoral species have suffered regional extinctions in the eastern Pacific with populations still present in the Indo-Pacific (Millepora platyphylla Hemprich and Ehrenberg, 1834) and eastern Indian Ocean (Millepora boschmai de Weerdt and Glynn, 1991). Considering the large numbers of obligate symbionts and other coral reef metazoan associates, there is a strong likelihood of large-scale extinctions following the loss of reef-building corals.
- Bonin, M.C., Almany, G.R., and Jones, G.P. Contrasting effects of habitat loss and fragmentation on coral-associated reef fishes. Ecology 92(7): 1503-1512, 2011.
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Disturbance can result in the fragmentation and/or loss of suitable habitat, both of which can have important consequences for survival, species interactions, and resulting patterns of local diversity. However, effects of habitat loss and fragmentation are typically confounded during disturbance events, and previous attempts to determine their relative significance have proved ineffective. Here we experimentally manipulated live coral habitats to examine the potential independent and interactive effects of habitat loss and fragmentation on survival, abundance, and species richness of recruitment-stage, coral-associated reef fishes. Loss of 75% of live coral from experimental reefs resulted in low survival of a coral-associated damselfish and low abundance and richness of other recruits 16 weeks after habitat manipulations. In contrast, fragmentation had positive effects on damselfish survival and resulted in greater abundance and species richness of other recruits. We hypothesize that spacing of habitat through fragmentation weakens competition within and among species. Comparison of effect sizes over the course of the study period revealed that, in the first six weeks following habitat manipulations, the positive effects of fragmentation were at least four times stronger than the effects of habitat loss. This initial positive effect of fragmentation attenuated considerably after 16 weeks, whereas the negative effects of habitat loss increased in strength over time. There was little indication that the amount of habitat influenced the magnitude of the habitat fragmentation effect. Numerous studies have reported dramatic declines in coral reef fish abundance and diversity in response to disturbances that cause the loss and fragmentation of coral habitats. Our results suggest that these declines occur as a result of habitat loss, not habitat fragmentation. Positive fragmentation effects may actually buffer against the negative effects of habitat loss and contribute to the resistance of reef fish populations to declines in coral cover.
- Sweatman, H., Delean, S., and Syms, C. Assessing loss of coral cover on Australia's Great Barrier Reef over two decades, with implications for longer-term trends. Coral Reefs 30(2): 521-531, 2011.
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While coral reefs in many parts of the world are in decline as a direct consequence of human pressures, Australia's Great Barrier Reef (GBR) is unusual in that direct human pressures are low and the entire system of similar to 2,900 reefs has been managed as a marine park since the 1980s. In spite of these advantages, standard annual surveys of a large number of reefs showed that from 1986 to 2004, average live coral cover across the GBR declined from 28 to 22%. This overall decline was mainly due to large losses in six (21%) of 29 subregions. Declines in live coral cover on reefs in two inshore subregions coincided with thermal bleaching in 1998, while declines in four mid-self subregions were due to outbreaks of predatory starfish. Otherwise, living coral cover increased in one subregion (3%) and 22 subregions (76%) showed no substantial change. Reefs in the great majority of subregions showed cycles of decline and recovery over the survey period, but with little synchrony among subregions. Two previous studies examined long-term changes in live coral cover on GBR reefs using meta-analyses including historical data from before the mid-1980s. Both found greater rates of loss of coral and recorded a marked decrease in living coral cover on the GBR in 1986, coinciding exactly with the start of large-scale monitoring. We argue that much of the apparent long-term decrease results from combining data from selective, sparse, small-scale studies before 1986 with data from both small-scale studies and large-scale monitoring surveys after that date. The GBR has clearly been changed by human activities and live coral cover has declined overall, but losses of coral in the past 40-50 years have probably been overestimated.
- Fung, T., Seymour, R.M., and Johnson, C.R. Alternative stable states and phase shifts in coral reefs under anthropogenic stress. Ecology 92(4): 967-982, 2011.
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Ecosystems with alternative stable states (ASS) may shift discontinuously from one stable state to another as environmental parameters cross a threshold. Reversal can then be difficult due to hysteresis effects. This contrasts with continuous state changes in response to changing environmental parameters, which are less difficult to reverse. Worldwide degradation of coral reefs, involving "phase shifts" from coral to algal dominance, highlights the pressing need to determine the likelihood of discontinuous phase shifts in coral reefs, in contrast to continuous shifts with no ASS. However, there is little evidence either for or against the existence of ASS for coral reefs. We use dynamic models to investigate the likelihood of continuous and discontinuous phase shifts in coral reefs subject to sustained environmental perturbation by fishing, nutrification, and sedimentation. Our modeling results suggest that coral reefs with or without anthropogenic stress can exhibit ASS, such that discontinuous phase shifts can occur. We also find evidence to support the view that high macroalgal growth rates and low grazing rates on macroalgae favor ASS in coral reefs. Further, our results suggest that the three stressors studied, either alone or in combination, can increase the likelihood of both continuous and discontinuous phase shifts by altering the competitive balance between corals and algae. However, in contrast to continuous phase shifts, we find that discontinuous shifts occur only in model coral reefs with parameter values near the extremes of their empirically determined ranges. This suggests that continuous shifts are more likely than discontinuous shifts in coral reefs. Our results also suggest that, for ecosystems in general, tackling multiple human stressors simultaneously maximizes resilience to phase shifts, ASS, and hysteresis, leading to improvements in ecosystem health and functioning.
- Adam, T.C., Schmitt, R.J., Holbrook, S.J., Brooks, A.J., Edmunds, P.J., Carpenter, R.C., and Bernardi, G. Herbivory, connectivity, and ecosystem resilience: Response of a coral reef to a large-scale perturbation. PLoS ONE 6(8): art. e23717, 2011.
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Coral reefs world-wide are threatened by escalating local and global impacts, and some impacted reefs have shifted from coral dominance to a state dominated by macroalgae. Therefore, there is a growing need to understand the processes that affect the capacity of these ecosystems to return to coral dominance following disturbances, including those that prevent the establishment of persistent stands of macroalgae. Unlike many reefs in the Caribbean, over the last several decades, reefs around the Indo-Pacific island of Moorea, French Polynesia have consistently returned to coral dominance following major perturbations without shifting to a macroalgae-dominated state. Here, we present evidence of a rapid increase in populations of herbivorous fishes following the most recent perturbation, and show that grazing by these herbivores has prevented the establishment of macroalgae following near complete loss of coral on offshore reefs. Importantly, we found the positive response of herbivorous fishes to increased benthic primary productivity associated with coral loss was driven largely by parrotfishes that initially recruit to stable nursery habitat within the lagoons before moving to offshore reefs later in life. These results underscore the importance of connectivity between the lagoon and offshore reefs for preventing the establishment of macroalgae following disturbances, and indicate that protecting nearshore nursery habitat of herbivorous fishes is critical for maintaining reef resilience.
- Graham, N.A.J., Nash, K.L., and Kool, J.T. Coral reef recovery dynamics in a changing world. Coral Reefs 30(2): 283-294, 2011.
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Coral reef ecosystems are degrading through multiple disturbances that are becoming more frequent and severe. The complexities of this degradation have been studied in detail, but little work has assessed characteristics that allow reefs to bounce back and recover between pulse disturbance events. We quantitatively review recovery rates of coral cover from pulse disturbance events among 48 different reef locations, testing the relative roles of disturbance characteristics, reef characteristics, connectivity and anthropogenic influences. Reefs in the western Pacific Ocean had the fastest recovery, whereas reefs in the geographically isolated eastern Pacific Ocean were slowest to recover, reflecting regional differences in coral composition, fish functional diversity and geographic isolation. Disturbances that opened up large areas of benthic space recovered quickly, potentially because of nonlinear recovery where recruitment rates were high. The type of disturbance had a limited effect on subsequent rates of reef recovery, although recovery was faster following crown-of-thorns starfish outbreaks. This inconsequential role of disturbance type may be in part due to the role of unaltered structural complexity in maintaining key reef processes, such as recruitment and herbivory. Few studies explicitly recorded potential ecological determinants of recovery, such as recruitment rates, structural complexity of habitat and the functional composition of reef-associated fish. There was some evidence of slower recovery rates within protected areas compared with other management systems and fished areas, which may reflect the higher initial coral cover in protected areas rather than reflecting a management effect. A better understanding of the driving role of processes, structural complexity and diversity on recovery may enable more appropriate management actions that support coral-dominated ecosystems in our changing climate.
- Watling, L., France, S.C., Pante, E., and Simpson, A. Biology of deep-water octocorals. Advances in Marine Biology 60: 41-122, 2011.
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Although deep-sea corals have been known to a handful of scientists and a large number of fishermen for at least two centuries, it is only over the last decade or so that there has been a surge of interest in their biology and ecology, largely a result of conservation concerns connected to the increasing exploitation of deep-sea resources. In this review we document what is known about taxonomy, phylogeny, biogeography, ecology and reproductive biology of deep-sea octocorals (Cnidaria, Anthozoa, Octocorallia) and highlight areas where knowledge is especially lacking. Most families (30 of 45) of octocorals have representatives living in the deep sea, and some families are restricted to, or show a diversity maximum, below 200 m. In particular, the calcaxonian families Chrysogorgiidae, Isididae, and Primnoidae are common, abundant and diverse in deeper waters, and available genetic data suggest they underwent an extensive in situ deep-sea radiation from a common ancestor. Many genera are widely distributed in the North Atlantic and the Pacific Oceans, however the patterns are incomplete because relatively few specimens have been collected in the South Atlantic, Indian, eastern Pacific, and Southern Oceans. Much of the taxonomy of deep-sea octocorals comes from the late 19th- and early 20th centuries and an inherent problem is that many species are known only from their type material, which in most cases consists of just a few specimens, and thus many genera are in need of revision. Increased collection and taxonomic revision will most likely alter our understanding of deep-sea octocoral biogeography. Many deep-sea octocoral colonies are long-lived (to more than 400 years) and large (10–500 cm in height) and provide a wide range of biogenic habitats to other invertebrate species. Most of the known invertebrate symbionts are commensalistic, and appear to live on a narrow range of host species. Conversely, symbionts may be quite rare on some deep-sea octocoral species. The most commonly observed symbionts come from the phyla Cnidaria, Annelida, Mollusca, Arthropoda (Crustacea), and Echinodermata. There is a general paucity of knowledge about reproductive processes in deep-sea octocorals, although it is clear they exhibit sexual reproductive strategies in common with their shallow-water counterparts. In all deep-sea species so far examined, gonochorism predominates at the colony level, and gonadal asynchrony seems to be the rule. Modes of asexual reproduction (budding, fission, parthenogenesis, etc.) that occur frequently in many shallow-water species have yet to be observed among deep-sea octocorals. Deep-water octocorals are of conservation concern. They are a common component of benthic communities on seamounts and ridges throughout the world, and are known also from continental and island slopes, especially in canyons. Loss of coral communities has been documented where bottom trawls have been used to catch a variety of deep-sea fish. Deep-water octocorals are one of the primary groups of organisms covered under the term "vulnerable marine ecosystem" (VME) and it is, therefore, important that we document their taxonomic diversity and understand aspects of their biology so that management can be better informed and these long-lived organisms protected.
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